An Electronic Correlation Approach to the Metal–Insulator Transition in the Half-Metallic Sr2FeMoO6Compound Doped With W

Abstract

The ferromagnetic double perovskite Sr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> FeMoO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> (SFMO) system with half-metallicity and fairly high Curie temperature points to the possibility of designing spintronics materials operating at room temperature. On the other hand, the double perovskite Sr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> FeWO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> is an antiferromagnetic insulator with the W(5d) states located at high energies and also with completely different magnetic and electronic properties than the ferromagnetic SFMO. The ferromagnetism and half-metallicity in SFMO have been explained within a strongly correlated picture, in which Fe <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> (3d <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> ) are localized spins in a high-spin S = 5/2 configuration and Mo <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5+</sup> (4d <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup> ) cores have one itinerant electron per formula unit (f.u.), which can hop to Fe sites only with an orientation antiparallel to that of the localized spin, thus stabilizing a ferromagnetic arrangement of local spins and fully opposite spin-polarized itinerant electrons. In this work, we study the effect of cationic doping on the behavior of \textT <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</sub> in SFMO with the Mo ions replaced by W ions, which leads to a metal-insulator transition. We use Green's function technique and the renormalization perturbation expansion method, in which the localized Fe spins and conduction Mo electrons interact via a double-exchange-type mechanism and the Hubbard model. Electronic correlations among the conduction electrons are included within a dynamical mean-field approach. Our results show a metal-insulator transition for W doping around x=0.2 in good agreement with experiments.